Development of the
series Yak-7A, the Yak-7B was better armed and
featured number of other improvements. Rifle-caliber
ShKAS
machineguns were replaced by far more capable pair of 12.7mm synchronized
UBS (left with 260 rounds, right with 140). To accommodate
those machineguns, Yak-7B had distinctive fairings on the engine cowling. As an option,
six RS-82 rockets could be replaced by two bombs (from 25 to
100kg each).

On the Yak-7B full package of airdynamic
TsAGI
recommendations was implemented:

Engine air intakes was made flush with wing surface, enlarged and turned slightly downwards

Protecting mesh was tilted and moved deeper into intake

Intake channels were carefully sealed

Tailwheel was completely retractable and covered with two side doors (like on the
UTI-26)

Wheel doors, access hatches, engine cowling were better fitted

Surface finishing quality was improved

Takeoff engine rate and propeller regime were modified in order to improve takeoff
performance. Oil and water cooler channels and shutters were revised, allowing continuous operation
with maximum engine power. Externally those changes may be identified by turned downwards outlet of the
oil cooler ('beard'). Some efforts were made to overcome oil leakage problem of the
M-105 engine, but with little success. Emergency pneumatic
system was extended to wheel brakes and landing flap, increasing aircraft reliability. Emergency air
bottle was relocated under cabin floor.
Cockpit also was revised:

Control stick R-1 similar to one of the Bf-109 was installed

Sliding section of the canopy was strengthened

Modification of the electric system included:

Lowered voltage on the control panel light, improving their reliability

Single-wire system with adequate grounding and shielding

As a result, range and quality of radio communication finally matched
VVS demands

Electro-pneumatic weapons control

Parking grounding introduced

All Yak-7B were equipped with radio receiver RSI-4 'Malutka' and
had provision for the RSI-3 'Oriol' transmitter. Nonetheless, shortage of transmitters
forced factory to fit only fraction of fighters with full set of radio equipment. For example,
only 10% Yak-7B of the 22th batch carried transmitters.

Despite Yak-7B was heavier than its predecessors, carried antenna mast and
fairings on the engine cowling, its performance was (finally!) identical with the
UTI-26-2, what was a 'milestone' in the Yak-7 evolution.
With new weapons, Yak-7B salvo was superior to all domestic single-engine fighters and most of
the enemy aircraft (Bf-109F and Bf-109G-2).

The first series Yak-7B ('golovnoj') N°14-13 passed combined State and
Factory Trials between January 28 and February 5
1942
at the Novosibirsk Factory N°153
airfield. Trials brigade included pilots A.G.Kochetkov (NII VVS)
and N.S.Rybko (LII), leading engineers V.N.Saginov (LII),
A.T.Stepanets (NII VVS) and A.P.Rybchenkov (Factory N°153),
weapon specialists A.G.Aronov (NII VVS) and G.I.Goudimenko (A.S.Yakovlev OKB). Trials were
quite short: 27 flights, totalling just 17h. The only revealed shortcoming was and
increased tendency to noseover.

It was clear that aircraft is a success,
and the GKO immediately ordered Factory N°153
to cease production of the Yak-7A in favour of new
'family member'.

Yak-7B M-105PA was built in April-July
1942,
with total 261 aircraft assembled. Little
new changes were introduced during this period. Since May 10 the
RS-82 launchers were deleted, because larger firepower
improved efficiency of Yak-7B attacks against bombers and ground targets. Increasing production
of the specialized Il-2 attackers allowed to use Yak-7B
in its major role - air-to-air combat.

Another change was an installation (May 20) of additional 80l fuel
tank in the rear cockpit. This tank was intended to counterweight increased weapons weight,
but at the same time it increased the weight and vulnerability (it was unprotected!). Naturally,
it was disliked by pilots, and was often removed by field mechanics. This 'field modification'
was approved (post-factum) by the GKO at the end of October
1942.

Special weapons trial was carried out in June
1942,
when series Yak-7B N°22-03 performed
25 flights (7h57min), firing its guns from under variety of conditions.

Yak-7B M-105PA were used during Kuban` and Stalingrad battles. Pilots and
commanders agreed that its combat performance is superior to all domestic fighters
(LaGG-3 and MiG-3
especially). It is also superior to Bf-109 in horizontal combat and almost even in vertical
maneuvers (depending on the Bf-109 model). List of shortcomings included:

Heavy, insufficient engine power, slow acceleration

Large drag induced by oil and water coolers

Poor rear view

Poor quality of canopy glazing (plexiglas), forcing pilots to fly with open cockpit

Demanding to airstrip length and quality

The most compliant with Stepanets description drawings of Yak-7B are found at
Gordon. Most of photos I found depicts a Yak-7A with partially covered tailwheel and no UBS fairings.
Some drawings show Yak-7B with fully covered tailwheel and UBS fairings, but with Yak-7A style engine
air intakes.